1. Field of the Invention
This invention is directed toward an improved spring compressor.
The invention is more particularly directed toward an improved spring compressor for use in servicing MacPherson strut assemblies which assemblies are used in car suspensions.
2. Description of the Related Art Including Information Disclosed Under CFR SS 1.97-1.99
MacPherson strut assemblies comprise a shock absorber mounted within a coil spring. The shock absorber has a bottom spring plate fixed to it, intermediate its ends. A top mounting plate is detachably connected to the top end of the shock absorber. The coil spring is mounted, under compression, between the bottom spring plate and the top mounting plate.
The shock absorber in the strut assembly often needs replacement. To replace the shock absorber it is neceessary to first additionally compress the spring to take the load off the top mounting plate, to then disconnect the top mounting plate from the shock absorber, and to the withdraw the shock absorber from within the spring. A new shock absorber is then inserted into the spring, the top mounting plate is connected to the new shock absorber and the spring is decompressed to be held, still under some compression, between the top mounting plate and the bottom spring plate on the new shock absorber. Often, the top mounting plate must also be replaced at the same time as the shock absorber because of rusting, or because of wear of a bushing employed with the top mounting plate.
The tool most commonly used in changing the shock absorber in a MacPherson strut assembly is a spring compressor that employs two threaded rods. Each rod carries a pair of opposed, facing hook members on it. To employ the compressor, the rods are placed on diametrically opposed sides of the coil spring on the strut assembly, parallel to its longitudinal axis. The facing hook members on each rod are placed over a section of a coil of the spring so as to loosely grip a substantial portion of the spring between them. The rods are now alternatively turned to draw the hook members on each rod toward each other to compress the mid-section of the spring between them. Once the mid-section of the spring has been compressed, the top mounting plate can be disconnected from the shock absorber and the shock absorber can be withdrawn from the spring. An example of such a spring compressor is shown in U.S. Pat. No. Re. 34,097. This type of spring compressor is simple and inexpensive. It is safe. It allows the shock absorber to be removed without having to release the spring. It also allows the top mounting plate to be replaced, if needed, without having to release the spring. It can be used on any size of spring. However this type of compressor is very, very slow to use because of the thread mechanism used to draw the hook members together, and because two rods, each with a thread, are employed. Also, the compressor is subjected to a lot of wear because of the load on the threads, particularly if a power wrench is employed to try to speed up the spring compressing and decompressing operation, and this wear, resulting in loose hook members, may cause the compressor to become unsafe to use.
In an attempt to reduce the time it takes to change the shock absorber on a MacPherson strut assembly it is known to provide spring compressors which use fluid moving means such as a pneumatic cylinder in place of the threaded rods. Examples of such spring compressors are shown in U.S. Pat. Nos. 3,814,382 and 4,395,020 by way of example. These compressors normally employ platens with one platen being fixed and the other movable. The strut assembly is mounted in the compressor with the bottom spring plate on the assembly on the fixed platen and with the top platen hooked over the top of the spring just below the top mounting plate. Movement of the top platen by the air cylinder will compress the spring allowing the top mounting plate to be disconnected. The air cylinder is moved again in the opposite direction to now release the spring so that the shock absorber can be replaced. Once the shock absorber is replaced, the spring is compressed again so that the top mounting plate can be reconnected to the shock, and the spring is then again released leaving it compressed between the top mounting plate and the bottom spring plate. However, the double compression and release operations still take time. In addition, the use of an air cylinder requires an air compressor making the spring compressor more expensive and not self contained. Platens are used with a single fluid cylinder since they apply pressure generally equally on both sides of the spring at each end and since they can be used with different sizes of springs. However, the platens have a disadvantage in that it is very difficult to mount the strut assembly between them, particularly at the top of the assembly because of the angle of the spring coils. More difficulty is encountered in mounting assemblies between the platens because the assemblies have springs have various diameters and angles. The use of air cylinders can also make it difficult to load the assemblies because of their quick jerky movements in positioning the movable platen. In addition, the platens are not as safe as hooks in holding the assembly while the spring is compressed and additional means must be employed to ensure that the spring does not pop out from between the platens when compressed.
A spring compressor that makes it easier to load the strut assembly, and that also uses hooks on the upper platen to hold the spring, is shown in U.S. Pat. No. 5,031,294. In this patent, in which the strut assembly is mounted upside down, the lower end of the spring adjacent the bottom spring plate, is held by two hook members, each mounted on an arm. The arms in turn are mounted on a frame in a manner allowing them to be moved toward or away from each other. In addition, the frame can be tilted about a vertical support post. This arrangement permits easier loading of the strut assembly, at least at one end, and, in using hook members at the top, makes the compressor somewhat safer. However, the use of a platen on the lower end still makes it difficult to mount the assembly and also the assembly is still somewhat unsafe because the assembly is not as securely held at its lower end. In addition, the spring must be fully decompressed in order to replace the top plate. It is noted that this compressor uses a screw member to apply pressure. The use of the screw mwmber makes it easier to load the strut assembly since there can be fine adjustment of the frame. However, the use of the screw assembly makes this compressor very slow to use.